In the field of electrophotographic color printing, one conventional approach to developing a color image on an organic photoconductor and then transferring the developed color image to an adjacent print medium is to use a so-called intermediate transfer member (ITM) which is located between a surface of the organic photoconductive drum and the surface of the print medium. Using this approach, liquid toners of cyan, yellow, magenta, and black are first transferred electrostatically in series from a conventional source of liquid toners to the surface of the organic photoconductor and then developed thereon such as by writing the desired color image with a controlled laser beam or other suitable light source. Color liquid toners are generally well known in the art of electrophotographic printing and are described in some detail, for example, in U.S. Pat. Nos. 4,925,766 and 4,946,753 issued to Elmasry et al and entitled "Liquid Electrophotographic Toners", both incorporated herein by reference.
When each of the colors of cyan, yellow, magenta, and black are individually developed on the organic photoconductive drum, the intermediate transfer member is then brought into intimate contact with the surface of the drum and is rotated against the drum surface to thereby transfer the written color images from the surface of the photoconductive drum to the intermediate transfer member. One example of a printing process using an intermediate transfer member in the transfer of the image from the photoconductive drum to the print media disclosed in U.S. Pat. No. 4,286,039 issued to Landa et al and incorporated herein by reference.
The use of the above described intermediate transfer member has been required in the above conventional electrophotographic color printing apparatus because of the fact that intimate contact between the toner and the print surface receiving the toner was essential for high quality transfer of the image from the surface of the photoconductive drum. The requirement for the use of this intermediate transfer member not only added cost and complexity to the electrophotographic printing apparatus, but it also brought with it critical alignment, reliability, and associated maintenance problems. In addition, since the developed liquid toners formed on the surface of the photoconductive drum were in discrete particle form and not held together satisfactorily within a properly charged unitary cohesive structure, prior attempts to transfer the color toners directly from the photoconductive drum to the print medium failed to completely transfer all of the developed toners to the print medium, thereby resulting in an unacceptable print quality.